Secret signaling system



(3. S. VERNAM.

SECRET SIGNALING SYSTEM. APPLICATION FILED SEPT. 13. mm.

Patented July 22, 1919.

2 SHEETS-SHEET l.

IN VEN TOR.

ATTORNEY 'ms COLUMBIA PLAnonRAPN cu., wAsHlNnroN, n c

6. S. VERNAM.

SECRET SIGNALING SYSTEM.

APPLICATION mu) SEPT. 13. mm.

Patented July 22, 1919.

2 SHEETS-SHEET 2.

IN V EN TOR. 61 61 %mam/ 2, fie/2.,

A TTORNEY "rm; COLUMBIA PLANOGIAPH c0.. WASHINGTON. D. c.

UNITED STATES PATENT OFFICE.

GILBERT S. VERNAM, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONEAND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

SECRET SIGNALING SYSTEM.

Application filed September 13, 1918.

To all whom it may concern:

Be it known that I, Glncnn'r S. VERNAM, residing at Brooklyn, in thecounty of Kings and State of New York, have invented certainImprovements in Secret Signaling Systems, of which the following is aspecification.

This invention relates to signaling sys tems and especially to telegraphsystems. Its object is to insure secrecy in the transmission of messagesand, further, to pro vide a. system in which messages may be transmittedand received in plain characters or a well-known code but in which thesignaling impulses are so altered before transmission over the line thatthey are unintelligible to anyone intercepting them.

The invention is here illustrated as applied to a well-known form ofprinting telegraph systems but, as will be readily understood, it isapplicable to other signaling systems. The invention will be more fullydescribed in connection with the accompanying drawings, in which Figure1 illustrates circuit arrangements at one end of the line in a systemembodying the invention, and Figs. 2 and 3 show modifications in thecircuits of the sending apparatus.

Like sending and receiving apparatus is located at each end of the line.Normally the message is recorded by both the local and the distantreceiving apparatus and since their operation is identical it will beunnecessary to show and describe the oppositc end of the line.

Referring to Fig. 1, A and B represent the transmitting and receivingfaces respectively of a known form of distributor used in printingtelegraph systems. Only such parts of the distributor and such parts ofthe circuit of the known "apparatus are here illustrated as arenecessary to an understanding of the resent invention. Accordingly onlytwo 0? the usual four rows of segments on the distributer are shown. Theouter row on the transmitting side comprises five segments 1, 2, 3, 4:and 5 from which the code impulses are transmitted. It also includes thesegment 6 on which the distributor arm normally rests, and the startingsegment S. The inner contact ring 7 is continuous and is connected toone side of the transmitting circuit 9 which is normally closed througha. suitable source of current not shown. The distributor arm 10 carriesa brush 11 Whose opposite ends con- Specification of Letters Patent.

Patented July 22, 1919.

Serial No. 253,962.

tact with the ring 7 and the segmental contacts repectively. When theapparatus is at rest this arm is detained by the latch 12 which may bewithdrawn by means of mag net 13 under the control of the operator. Thereceiving side of the distributer has five segments 1, 2, 3', 4' and 5,corresponding to the five sending segments but shortened to receive onlythe central part of the current impulses transmitted. It also has acontact 6', upon which the distributer arm normally rests, and a contactP for controlling the energization of a relay whose purpose will appearhereinafter. The re ceiving distributor arm 10 carries a brush 11 and iscontrolled by a latch 12 and mag net 13 as in the case of thetransmitting distributor arm.

The sending relays commonly used in the form of printing telegraphsystem here shown are indicated at 14, 15, 16, 17 and 18. The circuitscontrolled b i these relays ordinarily run directly to the distributorseg ments 1 to 5 for transmitting the signal impulses. In accordancewith this invention, however, these sending relays control the circuitsto the distributor segments through another set of relays 19, 20, 21, 22and 23 which may be called cipher sending re lays. The circuits throughthe contacts of relays 1a to 18 accordingly run from the source ofcurrent 24 through the windings of the rela s 19 to 23 and thence to anau tomatic cip ering device D.

The relays 14 to 18 are under the control of a sending device hereindicated at C as a known form of keyboard transmitter, which isprovided with a set of contacts 25, 26, 27, 28 and 29, these being underthe control of the key levers of the keyboard; as is well understood.The circuit of each of the relays 14 to 18 runs from ground through oneof these contacts and to a source of current 30. The relays are inactual practice provided with looking windings, not shown, whichfacilitate the transmitting of the message; andtheir circuits arefurthermore usually arranged to be. transferred at will to the contactsof a tape transmitter Which may be used instead of the keyboardtransmitter, all as is now well known in the art. The circuit of each ofthe relays 19 to 23 is provided with a branch to ground through aresistance 31, to enable the relays to be controlled by the cipheringdevice as will appear hereinafter.

For automatically ciphering the message a. well-known form of tapetransmitter I) may be employed. This transmitter, is provided as usualwith two bus-bars 32 and 33, connected respectively to battery andground at 34 and respectively. Five contacts 36, 31', 38, 39 and 40vibrate between these bus-bars under the control of a perforated tape ina well-known manner, and the circuits of the five relays 19 to 23 run tothese five contacts respectively, so that the energization of the relaysdepends upon the combined action of the normal transmitter C and theciphering transmitter D.

The apparatus for receiving the message at the other end of the line is,as above stated, in all respects like that shown at the right hand endof Fig. 1 and it will therefore be explained by reference thereto. Inorder that the message may be received in plain characters the printer(not shown) is operated through a set of receiving relays 42, 43, 44,and 46, which in turn are under the combined control of the line relay4.1 and the deciphering device D, the latter being the same instrumentas the ciphering device at the sending end of the line, and at the otherend a similar device operating synchronously and with an identicalcontrol tape. The windings of relays 42 to 46 are connected on one sideto the contacts 36 to 10 respectively of the ciphering device I), and onthe other side to the segments 1 to 5 of the receiving distributor.

The line relay 41 controls the armature 48, which has front and backcontacts 49 and 50 connected to battery and ground respec tively. Aconductor 51 connects the armature 48 and the inner segment 52 of thedistributer, which is angularly co-extensive with the contacts 1' to 5'.The line relay also has an armature 53 which closes at proper intervalsthe normally open circuit of the starting magnet 13' of the distrlbuter.

The operating magnet 56 of the ciphermg and deciphering device is underthe control of the relay 57 which is ener ized from the distributercontact P, its win ing being con nected between the grounded contact anda source of current at the printer (not shown) whenever the brush 11passes over the contact P. The circuit of magnet 56 is thereby closedfrom ground at 58 to battery at 34 once for each revolution of thedistributor to feed the tape and set the contacts in a manner now wellunderstood in the art. It is obvious that the impulses to the cipheringand deciphering devices at opposite ends of the line may step the tapesforward only for every second or every third character transmitted, orat any other desired interval, instead of for each character.

If desired the ciphering device may be provided with apparatus to throwit into or out of operation at the will of the transmit ting operator.For this purpose I have shown a relay 60 provided with an operatingwinding 61 and a locking winding 62, the circuit of the locking windingbeing controlled by a relay (53. The circuits of windings 61 and 63which respectively throw the ciphering device into and out of operation,run to the printer and are arranged to be there connected to battery bypredetermined code signals transmitted over the line.

In the modification shown in Fig. 2, a series of cipher sending relays19, 20, 21', 22 and 23,provided with difierential windings, are used inplace of the relays 19 to 23, shown in Fig. 1. One end of each of thewindings may conveniently be grounded at the relay while the oppositeends of each pair are connected to the sending and ciphering devicesrespectively. The windings will neutralize each other when both areencrgized, but the strength of either winding is suflicient to operatethe relay when not op posed by the other. In this modification theground connections, through the resistance 31 shown in Fig. 1, areunnecessary and are therefore omitted. Otherwise the circuits for thisarrangement are the same as in Fig. 1.

In the modification shown in Fig. 3 the sending relays (let to 18) ofthe usual print ing telegraph system are omitted and the circuits of therelays 19 to 23 are run directly to contacts 64, 65, 6G, 67 and 68 of atape transmitter C of known form whose bus-bars 69 and 70 are connectedto battery and ground respectively. It will be seen that thisarrangement, while simplifying the circuits, is not as convenientlyapplicable to the known form of printing telegraph system indicated inFig. 1, in which the relays 14 to 18 are already present and arranged tobe operated from either a keyboai d transmitter or a tape transmitter,depending upon the position of a switch controlled by the operator. Byconnecting the relay windings directly to a transmitter, as in Fig. 3,these windings will always be connected either to ground or to batteryat each end and no separate set of grounded connections as in Fig. 1, isnecessary.

The operation of the system shown in Fig. 1 is as follows: The sendinarm of the distributor will be started in the usual manner through theoperation of the ma net 13 and will transmit an open or start lmpulse asit passes over the segment S of the distributer. This 0 ens the circuit9, thereby deenergizing t e line relay 41, which permits switch 53 toclose, whereupon magnet 13 of the receiving distributor is energized.This releases the arm 10 which starts to rotate in approximatesynchronism with the sending arm 10. The start impulse of course putsinto operation the receiving distributer at both ends ofthe linesimultaneously, or at any other station which may be connected into theline circuit.

Let us suppose that the first character of the message to be transmittedis A. The code signal of A is ++f, Where represents an open or spacingimpulse and represents a closed or marking impulse in the system hereillustrated, although it will be understood that ositive and negativecurrent impulses may e used instead of closed and open circuit 0 erationif desired. For ciphering and deciphering the message the cipheringdevices at the opposite ends of the line are provided with identicalsections of tape upon which are recorded a series of code signals whichare preferably selected at random but if desired may themselvesrepresent a predetermined series of letters or Words. Let us supposethat the letter B happens to be in the ciphering transmitter at the samemoment that the letter A is being sent from the normal transmitter. Thecode for the letter B is The sending of A from the normal transmittermeans that the contacts 25 and 26 will be closed, While the contacts 27,28 and 29 are open. Thus, rei ays 14 and 15 will be energized and closetheir contacts, while relays 16, 17 and 18 remain unergized. Thepresence of the letter B in the code transmitter means that contacts 36,39 and 40; representing the plus impulses for B, will be in contact withthe bus-bar 32, which is connected to battery and that contacts 37 and38, re resenting the negative impulses for this 0 aracter will be incontact with bus-bar 33 which is grounded.

As a result of this combination of contacts in the two transmitters, itwill be seen that the relay 19 is connected at both ends tobattery; thatrelay 20 is connected at one end to battery at 24 and at the other endto ground at 35; that relay 21 is connected at one end to ground throughthe resistanc 31, and at the other end to ground at 35; that relay 22 isconnected at one end to ground through resistance 31, and at the otherend to battery at 34, and that relay 23 is connected to ground throughthe resistance 31 at one end and the battery 34 at the other. Therefore,relays 20, 22 and 23 will close their contacts, and relays 19 and 21will remain open. Consequently, as the distributer arm 10 rotates overthe contacts 1 to 5, impulses will be transmitted to the line fromcontacts 2, 4 and 5 and none from contacts 1 and 3. This means that thesignal will be transmitted over the line and this signal represents theletter G andnot the letter A which is the character of the message to betransmitted.

The transmitted impulses will be received at the distant end of the lineand at the receivin apparatus of the local station in ex actly the samemanner, since both are operating with identical ciphering tapes. Areference to the operation of the receiving apparatus B will, therefore,serve to explain the operation at the distant end.

The character to be recorded at the printer depends upon the combinationof impulses transmitted to it over the conductors 47. These conductorsrun to ground throu h the normally open'relay contacts of the re ays 42to 46, and these relays are under the joint control of the contacts ofthe device D and the contacts 49 to 50 of the line relay 41. Thus inreceiving the transmitted signal above referred to, the absence of animpulse over the line when the transmitting distributer passes thecontact 1, leaves the line relay 41 unenergized. The switch 48 istherefore on the back or grounded contact 50. Hence, when the receivingdistributer arm passes over the contact 1, the circuit of the relay 42Will be closed from battery 34 through contact 36 of device D, relaywinding 42, contact 1, brush 11, segment 52, conductor 51 and to groundat 50. When the distributer arm is passing over the contact 2', the linerelay 41 will be energized, due to an impulse transmitted from contact 2of distributer A through the contact of relay 20. Switch 48 willtherefore be on its front or battery contact 49 and relay 43 willtherefore be energized, being connected at one end to the battery 54 andat the other end to ground at 35. When the distributer arm is passingover contact 3 the line relay will be again unenergized and the switch48 upon its grounded contact and the relay 44 will therefore remainunergized, since it will be connected to ground at both ends. While thearm is passing over contacts 4 and 5 the line relay 41 is energized, dueto impulses through the contacts of relays 22 and 23, so that switch 48is upon its front or battery contact, and relays 45 and 46 thereforeremain unergized, since they are connected at both ends to battery. Inother words, relays 42 and 43 are successively closed and transmitimpulses to the printer, while relays 44, 45 and 46 remain open.

The code signal upon which the printer operates is therefore, which isthe symbol for the letter A and the printer accordingly prints theletter which it was desired to transmit.

As the distributer arm 10' passes the contact P, relay 57 is energizedwhich closes the circuit of magnet 56, thereby feeding the tape one stepand readjusting the contacts of the ciphering and deciphering de vicefor the new ciphering letter. If it is desired to throw the cipheringand deciphering devices out of operation, the operator may transmit aprearranged signal as above suggested, thereby causing an i111- pulse topass from the printer through the winding of relay (53 to ground. Thisopens the circuit of the locking winding 62 of the relay 60, whichreleases its armatures and whereupon both bus-bars of the cipheringdevice will be connected to ground, bar 33 at 35, and bar 32 at thegrounded side of the battery 34. The take feed magnet 56 is likewiserendered inoperative. When it is desired to again throw the cipheringdevice into operation, another predetermined signal is transmitted,whereupon an impulse passes from the printer through the winding 61 ofthe relay 60 and to ground, which energizes the relay and reestablishesthe connections shown on the drawing.

The operation of the modification shown in Fig. 2 is the same as thatjust described except that the operation of the relays 19' to 23 willdepend upon the combined effect of their two windings instead of uponthe effect of the connections at the opposite ends of a signal winding.Thus if both of the windings of any relay are connected to battery atthe normal and ciphering transmitters respectively, the relay willremain unoperated because the magnetic effects of the two windings willneutralize each other. If they are both either open or grounded at theopposite ends, the relay will, of course, not, operate, but if eitherWinding is connected to battery while the other is grounded oropen-circuited, the relay will operate, and obviously the circuitconditions which make a relay operate in Fig. 1 will likewise make itoperate in Fig. 2. No separate description of the details'of theoperation in connection with this figure is therefore necessary. The useof the grounded differential windings does away with the necessity forthe resistances 31 shown in Fig. 1, since there is always a groundconnection for any winding connected at the.

opposite end to battery.

The operation of the modification shown in Fig. 3 will be clear from theforegoing description. The ends of the relay Windings 19 to 23, whichrun to the normal transmitter C will always be connected either tobattery or to ground, depending upon the position of the contacts 64 to68 and there is, therefore, no need of the resistances 31 shown in Fig.1.

The system as above described will therefore serve to change theimpulses of the character to be transmitted into another set of impulsesrepresenting some other character of the same code and anyone attemptingto intercept the message by tapping the wires will receive the im ulsesso altered. A consideration of the clrcuits will show that even if thecontacts of the eiphering transmitter are left in one position, a seriesof varying characters will be transmitted by the line which aredifferent from the characters of the message to be sent, while if thecontacts of the code transmitter are altered by shifting the tapethereof each time a letter of the message is to be transmitted, the ruleby which the variation is made will be changed for each letter, in otherwords the cipher employed will be changed for each letter transmitted.It will also be clear that the set of impulses actually transmitted mayrepresent some rinter operation other than the printing 0 a letter, suchas the line shift or carriage return when a letter is in the normaltransmitter. So that a printer tapped onto the line would show anindescribable confusion of signals unless it were provided with adeciphering device and was using the same deciphering tape as used atthe transmitting station.

It is obvious, of course, that the invention here disclosed is equallyapplicable to transmission through any known medium and is, therefore,suitable for either wire or wireless transmission. I

The forms of the invention here shown are illustrative only, as it willbe obvious that various modifications may be made without departing fromthe spirit of the invention or the scope of the appended claims.

What is claimed is:

1. The method of enciphering si als where the characters are re resentedi? a number of periods of di erent current values which consists inaltering the normal code impulses of a character to be trans mitted inaccordance with a rule represented by some other character in a likecode.

2. The method of transmitting messages where the characters are reresented by a number of periods of di erent current values, whichconsists in altering the normal code impulses of a. character inaccordance with a rule represented by some other character in a likecode, and restoring the transmitted impulses so produced to their normalcode form at the receiving end by altering the received impulses inaccordance with a rule represented by the same character.

3. The method of transmitting messages where the characters are reresented by a number of periods of di erent current values, whichconsists in alterin the normal code impulses of a character inaccordance with a rule represented by some other character in a likecode, restoring the transmitted impulses so produced to their normalcode form at the receiving end by altering the received impulses inaccordance with a rule represented by the same character, andcorrespondingly changing the rule of alteration and restoration at bothends of the line at frequent intervals.

4. The method of enciphering signals which consist in combining theeffect of elec trical conditions representing the message character,with the efl'ect of those representing a cipher-ing character, toproduce electrical impulses representing some other character.

5. The method of eneiphering signals which consists in combining theeffect of electrical conditions representin the message character, withthe effect 0 those rep resenting a ciphering character, to produceelectrical impulses representing some other character, and changing theciphering character from time to time.

6. The method of decipherin a secret message, which consists in comining the electrical effect of the received impulses with the efi ect ofthe electrical conditions representing a deciphering character toproduce electrical impulses representing the message character.

7. The method of deciphering a secret message, which consists incombining the electrical effect of the received impulses with the efiectof the electrical conditions repre senting a deciphering character toproduce electrical impulses representing the message character, andchanging the decipheri character at intervals, to correspond wittheciphering character used in transmitting the message.

8. The method of transmitting signals, which consists in producing a setof electrical conditions appropriate for transmitting a character of themessage according to an accepted code, producing a second set ofarbitrarily. chosen electrical conditions, combining the electricaleffects of the two sets of conditions to produce a third set ofelectrical conditions, and transmitting impulses corresponding to saidthird set of conditions.

9. The method of transmitting messages, which consists in producing aset of electri: cal conditions appropriate for transmitting a characterof the message according to an accepted code, producing a second set ofarbitrarily chosen electrical conditions, combining the electricaleffects of the two sets of conditions to produce a third set of electrical conditions, transmitting impulses corresponding to said third setof conditions and changing the second set of electrical,

conditions from time totime during the transmission of the messages.

10. The method of transmitting messages which consists in producing aset of electrical conditions appropriate for transmitting a character ofthe message according to an accepted code, producing a second set ofarbitrarily chosen electrical conditions, com b-ining the effects of thetwo sets of conditions to produce a third set of electrical conditions,transmitting impulses corresponding to said third set of conditions,producing at the receiving station a deciphering set of electricalconditions corrq sponding to said second set and combining theelectrical effects of these conditions with the electrical effect of thetransmitted impulses, to produce a set of impulses representing themessage character.

11. The method of transmitting messages which consists in producing aset of electrical conditions appropriate for transmitting a character ofthe message according to an accepted code, producing a set ofarbitrarily chosen electrical conditions of like kind for encipheringthe character, combining the effects of the two sets of conditions toproduce a third set of electrical conditions, transmitting impulsescorresponding to said third set of conditions, producing at thereceiving station a deciphering set of electrical conditionscorresponding to said second set, combining the electrical effects ofthese conditions with the electrical effect of the transmitted impulses,to produce a set of impulses representing the message character andcorrespondingly changing the enciphering and deciphering sets ofconditions at intervals.

12. The method of transmitting messages, which consists in producingelectrical conditions suitable for representing a character of themessage, altering the eflect of these conditions by and in accordancewith the electrical conditions representing some other character,transmitting impulses according to said altered effect and reproducingat the receiving end the original electrical conditions by altering theeffect of the transmitted impulses by and in accordance with electricalconditions representing the same character as the conditions used toeffect the alteration at the transmitting end of the line.

13. In an electrical signaling system, a set of contacts arranged to beclosed in accordance with a pro-determined code for representingcharacters; a similar set of contacts arranged to be closed in likemanner; a third set of contacts, means for closing any or all of saidthird set of contacts to correspond with the relative positions ofcorresponding contacts in said first and second mentioned sets, andmeans for transmitting impulses to the line in accordance with thearrangement of said third set of contacts.

14. In an electrical si nalin system, a set ofrelays for control ing t eimpulses transmitted to the line, means for connecting either end of anyrelay winding of said set to either pole of a current source, and meansfor transmitting impulses to the line in accordance with the circuitconditions produced by said relays under the varying connections fortheir windings thus produced.

15. In an electrical signaling system, a set of relays for controllingthe impulses transmitted to the line, two sets of windin terminals forsaid relays, means for app ying differing electrical potentials to theterminals in either set to make the sets correspond with predeterminedcode si nals one of which represents the message 0 aracters and meansfor transmittin impulses to the line in accordance with t e circuitconditions established by the relays.

I 16. In a signal transmitting system, two sets of contacts, any one ofwhich may be connected to either pole of a current source, wherebyeither set may represent any character of a code depending on thearrangement of its contacts, relays having windings connected betweencorresponding contacts 111 the two sets and means for sending currentimpulses through the contacts controlled by said relays.

17. In a device for automatically enciphering messages, the combinationof switching mechanism for making sets of electrical connections tocurrent sources of differing potential thereby representing thesuccessive characters of the message, other switching mechanism formaking other sets of electrical connections, circuits connecting thecorresponding contacts in the two sets of connections and meanscontrolled by the current in said circuits for governing the combinationof impulses transmitted to the line.

18. In a device for automatically deciphering messages, a combination ofswitching mechanism for making sets of electrical connectionscorresponding to the connections used in ciphering the message, meansresponsive to the received impulses for altering the condition of alocal circuit, and means for combining the effect of the electricalcondition of the local circuit under successive line impulses with theeffect of the conditions produced in said switching mechanism, whereby aset of impulses is created corresponding to the message character.

19. In a signal receiving instrument, switching mechanism fordetermining the code impulses to be recorded, a line relay responsive tothe received impulses, a set of terminals whose electrical conditionrelative to eachother may be varied to repre sent ciphering symbo s, andmeans under the combined influence of said relay and said set ofterminals for controlling said switching mechanism.

20. In a signal receiving instrument, a plurality of circuits forcontrolling the re- 1,ero,719

cording of characters, a relay for controlling each of said circuits, adeciphering device arranged to connect one terminal of each of saidrelays to either pole of a source of current, a distributor forconnecting the opposite terminal of each of said relays successively toa single circuit, and a line relay responsive to receive impulses forconnecting said single circuit to either pole of a source of current,according to the char actor of the impulse received.

21. In a signaling system, a main circuit, a plurality of branchcircuits, a distributor for connecting the main circuit with said branchcircuits successively, switching mech anism in said branch circuits fordetermining the character of the impulse transmitted over the maincircuit when connected to the respective branch circuits, twocontrolling devices either one of which may transmit impulsesrepresenting code characters, and connections between said controllingdevices and said switching mechanism whereby the switching mechanism maybe operated by said controlling devices separately or in accordance withtheir combined effect.

22. In a signal transmitting systennmeans for transmittin normal codeimpulses over the line, ciphering and deciphering devices at oppositeends of the line for automatically altering the impulses to transformthem into a different character and restoring them at the receiving endof the line, and means for throwing said devices into and out ofoperation by the transmission of predetermined signals over the line.

23. In .a signaling system, a main line, mechanism at each end of saidline for sending and receiving messages, ciphering and decipheringdevices at opposite ends of said line and associated with said mechanismfor automatically ciphering the message at the transmitting end and fordeciphering it at the receiving end, and means for throwing theciphering and deciphering devices into or out of operation in responseto the transmission of a predetermined signal over the line.

24. In a signal transmitting system, a sendiaig and receiving mechanismcomprising a set of relays controlling the impulses imposed upon theline, another set of relays for controlling the impulses sent to therecording mechanism, a ciphering and decipherin device connected to bothsets of relays w ereby the message to be sent is en- .ci'phered fortransmission and received messages are deciphered by the same device.

In testimony whereof, I have si ned my to this specification this twefth day of September 1918.

GILBERT S. VERNAM.

Copies of this patent may be obtained for five cents each, by addressingthe-Gommissioner of IPatents, Washington, D. 0.

